Analytical test elements are used in particular for the rapid qualitative and quantitative analytical determination of components of liquid samples, for example in the form of separate test strips or tape-like test material. For example, see test elements as disclosed in EP 1 039 298 B1 and EP 1 593 434 A2, the disclosures of which are each hereby incorporated herein by reference in their respective entireties. Analytical test elements can also be provided in integrated systems in which the test element is connected to a sampling device. The surface of the test element as a detection layer is typically prepared with suitable dry chemicals for the desired analysis. Important fields of use include for example medical diagnostics and environmental analysis.
Conventional test elements are usually manufactured from plastic in order to simplify their production and reduce production costs and for reasons of component stability. They therefore have a comparatively hydrophobic surface.
Methods for producing a surface coating and the uses of such surface coatings to increase the surface tension of objects are generally known. These objects can for example be an analytical test element on which sample liquid is transported from a sample application site to a determination site, where a detection site is downstream of the sample application site in the direction of transport. The surface coating is obtained by depositing a coat of at least one element that can be oxidized by water or an alloy that can be oxidized by water and subsequent action of boiling water or water vapor on the deposited layer. All those objects come into consideration as objects to be coated whose surface has a lower hydrophilicity in the uncoated state than in the coated, after-treated state such as plastic, metal, glass, ceramic, paper, fleece, cardboard etc. where the objects can be of any design e.g. planar, three-dimensional, porous etc. See, for example, DE 197 53 848 A1, the disclosure of which is hereby incorporated herein by reference in its entirety.
Hydrophilic surfaces can thus be generated in order that a sample spreads thereon as a result of wetting and therefore moves in a certain direction between two such surfaces driven by capillary forces. Both surfaces are topologically comparable, they are also functionally the same and do not touch. They typically serve to transport liquid from a sample application site to a determination site.
Because the aqueous sample should wet the surface well, the surface is provided with a spreading agent for this purpose, for example in the form of spreading nets coated with a wetting agent.
The use of spreading nets especially for test strips is known. They are usually fabrics, knitted fabrics, etc. made of plastic fibers which are provided with a surfactant coating for hydrophilization. Anionic or neutral surfactants such as for example DONS (docusate sodium) are usually used for this purpose. However, the quality of these coatings is subject to variations and becomes more difficult to realize the finer the material structure is. In particular zones of accumulation and depletion occur in a net due to capillary drying effects of a dissolved surfactant. In addition a number of surfactants have a tendency to creep.
Alternative methods have been proposed in which plastic surfaces are hydrophilized by planar coating with a metallic material and subsequent oxidation of the material with water. See, for example, EP 1 037 717 B1, the disclosure of which is hereby incorporated herein by reference in its entirety.
The object of the present invention is to provide generic test elements or filament structures with hydrophilicly modified surfaces which can be produced with the least possible effort and in a reproducible quality.